1. Field of the Invention
The present invention relates to a toner image forming apparatus.
2. Discussion of the Related Art
There are many proposals to print images on a print paper which are based on the Xerographic process, electrostatic recording process, magnetic recording process, or the like. Among those proposals, copying machines based on the Xerographic process and laser printers based on the combination of the Xerographic process and the laser scan exposure process have been widely used.
The simplex printing techniques are disclosed in Japanese Patent Unexamined Publication Nos. Hei. 3-228467, 3-221976, Japanese Patent Examined Publication No. Hei 3-18182, and Japanese Patent Unexamined Publication No. Sho. 55-83070. The duplex printing techniques are disclosed in U.S. Pat. Nos. 4,477,176 and 4,095,979. The disclosed duplex printing techniques, which are able to print images on both sides of a print paper, suffers from the following problems. The paper size available for the duplex printing is limited to only some specific sizes of paper. The mechanisms for the duplex printing are complicated in construction and poor in reliability.
Also, some techniques for forming a toner image of multi-color by the Xerographic printing method or an electrostatic printing method are disclosed in, for example, Published Unexamined Japanese Patent Application Nos. Hei. 2-302768 and Hei 4-5669 and U.S. Pat. Nos. 4,422,405 and 4,078,929.
In such conventional color printers, a latent electrostatic image is formed on an insulating recording media, such as a dielectric or photoconductive photo receptor, and is developed with developer containing colored particle toner, thereby forming a color image.
To form a color image of a multiple of colors by using a color printer based on the just-mentioned principle, the color toner images of used colors are formed repeatedly, and are composed into a single color toner image. In the color printer using four primary colors, for example, toner images of black, magenta, cyan, and yellow are formed, and these toner images of four colors are registered and composed into one color toner image of full color.
In the above-mentioned conventional color printer, compared with a monocolor printer, the toner image forming apparatus is complicated and expensive. Therefore, it can be used for only a limited number of fields.
Also, the color toner images must be registered with one another highly accurately.
Further, the conventional color printer takes a longer print time than the monochromatic printer. In the case of the color printer using four primary colors, for example, its print time is approximately four times as long as that of the monochromatic printer.
When a multi-color image is formed by the conventional color printer, color toner images of several colors are registered and composed into a single color image. High registration accuracy is not required for the formation of picture images. However, to form the characters and fine lines, high registration accuracy is required, practically, it must be at least within 0.07 to 0.1 mm. Therefore, characters and fine lines, when formed, sometimes suffer from color displacement.